Regensburg 2022 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 79: Surface Reactions and Heterogeneous Catalysis 3

O 79.5: Vortrag

Freitag, 9. September 2022, 11:45–12:00, H4

Deciphering the intramolecular C-C coupling mechanism of a model aryl radical via bond-level AFM imaging — •Qigang Zhong¹, Jannis Jung², Daniel Kohrs³, Daniel Ebeling¹, Doreen Mollenhauer², Hermann A. Wegner³, and André Schirmeisen¹ — ¹Institute of Applied Physics, Justus-Liebig University Giessen (JLU), Germany — ²Institute of Physical Chemistry, JLU, Germany — ³Institute of Organic Chemistry, JLU, Germany

Although on-surface dehalogenative and dehydrogenative C-C coupling has proved to be a versatile and prevailing approach to constructing atomically precise carbon-based nanostructures, understanding of the reaction mechanisms remains limited by the elusive intermediates. Here, we studied the intramolecular cyclodehydrobromination of 1-bromo-8-phenylnaphthalene on Cu(111) and Ag(111) using bond-level atomic force microscopy (BL-AFM). The reaction occurs at room temperature on both metal surfaces, while the reaction rate on Cu(111) is much higher than that on Ag(111) presumably due to the higher catalytic activity of copper. Surface-bound radicals, cyclized intermediates and dehydrogenated product were captured by BL-AFM imaging and verified by DFT calculations, suggesting a multi-step reaction process, i.e. debromination, radical cyclization and dehydrogenation. The large proportion (up to 65 percent) of cyclized intermediates on Cu(111) indicates that dehydrogenation is the rate-determining step, which is corroborated by DFT calculations of activation barriers. To achieve a reasonable activation barrier for dehydrogenation, multiple pathways were theoretically evaluated.